Lumber twists in the kiln

[Joe]

Hi, First time on the forum and new to drying wood. Some background, I just got our kiln up and running and ran two loads thru, drying mostly 8/4 lumber. The maple wants to twist when drying. Any suggestions on how to keep it from twisting.

[HencoV]

Quick answer....add a few tons of weights onto the stacks.

Not so quick...find out why it's warping. Get a kiln expert to come and have a look. The fee will probably pay for itself in quality retention in a few days/weeks

If you are the DIY type...start here... Not knowing maple...take this as "broad & general" advise. Any warp (bow, twist, spring, cup) is partly due to the inherent structure of timber, and/or caused my differential shrinkage, either across the face, thickness or the length of the board. In short, one section of the board shrinks more than the other, causing distortion. Bad drying practice makes it worse because some boards or areas of the stacks gets more exposure to hotter dryer air than others, drying out faster and shrinking more/quicker.

Bad drying can refer to physical factors...stacking, loading, baffling & maintenance.  Getting any one or more of these 4 wrong will result in uneven air flow and energy distribution through the stack and bad results. Get as close to 100% of the air through 100% of the timber..evenly. These should always be the first things to check, and must be a constant.

Next, get drying control and schedule right. It is possible that your schedule may be very harsh in the beginning. There is enough literature available to guide you on the web. Also speak to other dryers in your area drying similar timber

Good luck

[MichaelM]

Both Joe and HemcoV had some good suggestions.

If you are used to drying softwoods to 15%, the hardwoods may surprise you.  They are typically dried to 7-8, maybe 9% and there is a lot more warp simply due to the low MC.  Also, maple is a whole different animal than alder.  If you are familiar with alder, plan on the warp in maple being much greater.  In my comments here I am assuming that this is bigleaf or Oregon maple.

Schedule is important.  Something like schedule 80 in "Dry Kiln Schedules for Commercial Woods" (google this because the attachment will be too big to go though).  See back of attachment for proper equalizing and conditioning.  Allow 7-9 days and top out at 170 instead of 180.  You do need the big depression (50F) to get the MC low enough but will get better color at 170F.

This schedule is a MC-based schedule.  Google “Dry Kiln Operators Manual” or “Drying Hardwood Lumber” for this USDA-recommended method.

For specific questions, feel free to PM me.

[Joe]

Good suggestions. I tried banding the stacks, but they just got loose after about 15 days. I'll try some of the other thing with the next batch.